1. Field of the Invention
The present invention is directed to a release agent applicator. The release agent applicator applies parting liquid onto the surface of a fixing drum of an electrographic printer or copier device working according to the transfer printing principle.
2. Description of the Related Art
In electrographic printer or copier devices, charge images are generated on a charge image carrier, for example on a photoconductor drum, these images are then inked with a developer mix in a developer station on the basis of electrostatic or magnetic forces. The inked charge images are transfer-printed onto a recording medium which is in the form of single sheets or continuous stock, for example, of paper, in a transfer printing station and are subsequently thermally fixed. For thermal fixing, U.S. Pat. No. 3,324,791 discloses that a fixing station be provided with two drams between which the recording medium with the toner image is moved. The one fixing drum facing toward the toner image is heated, the other drum presses the recording medium with the toner image against the fixing drum. The toner is then melted into the recording medium by heat and pressure of the drums.
In order to prevent toner from remaining adhering to the surface of the fixing drum, the surface thereof is moistened with parting liquid, for example silicone oil. For applying this parting liquid onto the fixing drum, German Patent Document DE-C-39 42 147 discloses a release agent application means wherein an application element composed of felt is pressed against the fixing drum by a pressing member extending along the fixing drum. A dosing tube that contains discharge openings in its longitudinal extent is provided at that side of the application element facing away from the fixing drum. Release agent, or parting oil, that is pumped into the dosing tube emerges from the openings and thus proceeds onto the application element.
In order to be able to match the moistening of the surface of the fixing drum to the width of a recording medium, a rotatable control wedge is contained in the dosing tube. More or fewer discharge openings can be closed dependent on the position of this control wedge, as a result whereof the release agent is only output to the region of the fixing drum coming into contact with the recording medium. The position of the control wedge is always matched by a motor operator to the recording medium width processed in the printer or copier device.
It has now been shown that the adaptation of the oiling width must ensue very exactly. When too much release agent is output from the release agent dosing tube, then contaminations arise in the fixing station and neighboring units of the printer or copier device. When too little release agent proceeds onto the surface of the fixing drum, then print image disturbances arise. A satisfactory printing result can therefore only be achieved when the width matching of the release agent application functions reliably.
Due to its direct contact with the heated fixing drum, however, the release agent application means is exposed to high temperatures. These high temperatures also lead to a particular load of the motor for adjusting the control wedge in the dosing tube. This motor operator therefore often fails to perform.
German Patent Document DE-A1-3941 195 also discloses a release agent application means for applying release agent to the surface of a fixing drum of an electrographic printer or copier device that comprises a pressure member extending along the fixing drum and an application element lying against guide elements of the pressure member via which release agent is applied onto the fixing drum. A cannula that can be composed of porous textile fiber material is provided axially parallel to the application element for the delivery of the release agent.